Convertible blood clot filter

ABSTRACT

A vena cava blood clot filter is described that is attached to the walls of the vena cava by barbed anchors. In its filtering state, the filter is cone shaped which causes the blood to be filtered. The cone shape is formed by an appropriate restraining mechanism. When it is desired to stop filtering, the restraining mechanism is released and the filter takes a cylindrical shape. The cylindrical shaped filter will then line the vena cava wall and cease filtration of the blood.

BACKGROUND

[0001] 1. Field of Invention

[0002] The following invention relates to a clot filter and morespecifically to a convertible vena cava blood clot filter.

[0003] 2. Description of the Related Art

[0004] Vena cava blood clot filters are generally placed in the inferiorvena cava, introduced either through the femoral or jugular vein. Thesefilters trap blood clots that have arisen from the peripheral veins andthat travel through the vena cava. By trapping the blood clots, thefilter prevents the clots from lodging in the pulmonary bed, which canlead to a condition known as pulmonary embolus.

[0005] Pulmonary embolus (PE) has long been recognized as a major healthcare concern. Untreated PE is associated with a high mortality rate,widely held to be approximately 30%, although the exact rate is unknown.Symptomatic PE, however, represents only one manifestation of a moreprotean disorder, venous thromboembolic disease (VTD), which includesboth deep venous thrombosis (DVT) and PE. Understanding of theinterrelationship of these disorders has increased in recent years, ashas the extent to which VTD contributes to patient mortality.

[0006] The current standard of care of VTD is anticoagulation for aminimum period of six months. If patients are properly treated withanticoagulation, the impact of VTD upon patient health is minimized.However, anticoagulant therapy carries the risk of bleedingcomplications. In patients with VTD or PE that 1) are at high risk ofdeveloping a bleeding complication, 2) have a contraindication toanticoagulant therapy, 3) had a failure of response to anticoagulanttherapy (i.e. further episodes of PE), or 4) developed a bleedingcomplication because of anticoagulant therapy, vena cava blood clotfilters play an important role in the management of VTD.

[0007] Vena cava clot filters can be categorized into two devicefamilies: permanently implanted devices and temporary devices.Permanently implanted devices are implanted for patients that require afilter for more than fourteen days. Fourteen days roughly approximatesthe time before which the points where the filter contact with the cavalwall becomes covered by endothelial cells which thicken to eventuallyattach the filter permanently to the cava wall. If an attempt is made toremove the filter after this time point, severe damage may occurresulting in laceration or rupture of the vena cava, or at the veryleast, a focal disruption of the endothelial lining which may predisposeto caval stenosis, thrombosis (clot formation) or occlusion.

[0008] Since the permanent blood clot filters are left in the body forthe lifetime of the patient, the patient undergoes several risks thatcontinue throughout the person's lifetime. The reported long-termsequela of some of the permanent devices include thrombotic occlusion ofthe vena cava, filter migration, filter fragmentation and filterembolization.

[0009] These problems can occur because the blood clot filter isdirectly in the blood stream and continually filtering the blood clotsthroughout the lifetime of the patient. Thrombotic occlusion and filterembolization can occur when a gradual buildup of blood clots forms in oraround the filter due to the continuous filtering. Filter migration andfilter fragmentation can occur because of the constant impact betweenthe blood filter and the flowing blood can move the filter or break thestructure of the filter.

[0010] Temporary blood clot filters do not share those long-term risksbecause they are removed from the patient's body. However, thesituations in which temporary blood clot filters are used are limited.The patient must recover to the point that the risk from PE is reducedto an acceptable level prior to the 14-day limit or to a time point atwhich the patient may be safely anticoagulated. Otherwise, a permanentlyimplanted blood clot filter must be used to avoid damage to the cavalwall that may result if attempt is made in removal after 14-days.

[0011] Temporary blood clot filters fall into two categories. One grouputilizes a permanently attached tethering catheter for retrieval,whereas the other requires the use of a retrieval device for removal. Inaddition to the limited amount of time that it can remain in the venacava, the catheter-based design has the draw back of infectiouscomplications at the entry site. Other temporary designs allow a filterto be placed and later retrieved using a device.

[0012] When a patient's need for a blood clot filter is known to betemporary, but longer than the 14-day period, the patient's onlyrecourse is to receive a permanent blood clot filter. An example of atemporary need resulting in placement of a permanent vena cava bloodclot filter is a patient who need needs protection from PE in theperioperative period or a woman with DVT during pregnancy. Thesepatients will receive a permanent filter and be unnecessarily subjectedto the lifelong risks associated with permanent blood clot filters.

[0013] Accordingly, it is the object of the present invention todisclose an implanted device that provides effective caval filtrationfor any length of time. However, if and when it is determined that therisk from the implanted device disrupting laminar blood flow exceeds therisk of further PE, the filter can be removed from the blood stream toeliminate the associated risks of having a permanent filter within thebloodstream. This can be done at any time without regard to the amountof time that the filter has been implanted and without causing damage tothe caval wall. Another object of the present invention is to providesuch a filter that allows trapping (capturing) of blood clots of sizesthat result in a clinically significant PE that poses an unacceptablyhigh risk of patient morbidity and mortality. The trapped clots in thefilter are then dissolved by the bodies own intrinsic fibrinolyticsystem, without causing pulmonary function compromise. Still a furtherobject of the present invention is to provide such a filter that isrelatively simple in design and is relatively inexpensive tomanufacture.

SUMMARY OF THE INVENTION

[0014] The present invention provides a blood clot filter and a methodfor its use. The blood clot filter comprises an expandable filter shapedin the form of a cylinder. The filter is composed of high memory wireand the wire is formed into a band of zigzag bends.

[0015] In its pre-deployment form, both ends of the filter are collapsedto form a slender wire construct. After deployment, one end of thecylinder is held together by a suitable restraining means such as aTeflon ring with a diameter of approximately 3 mm. The other end of thecylinder is expanded and has a sufficiently large diameter to contactthe walls of the inferior vena cava with sufficient force to hold thefilter in place against the inferior vena cava. Additional means areused to attach that end of the filter to the walls of the vena cava.

[0016] When it is desirable to stop filtering, the Teflon ring holdingthe narrower end of the filter is broken thereby releasing the end ofthe filter. Once released, the narrow end of the filter will expanduntil the entire filter lines the walls of the vena cava. The filterwill no longer filter the blood nor will it be directly in the bloodstream.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The accompanying drawings are included to provide anunderstanding of the invention and constitute a part of thespecification.

[0018]FIG. 1 depicts a side view of a deployment device for the bloodclot filter in accordance with the present invention.

[0019]FIG. 2 depicts a side view of the first embodiment of a blood clotfilter deployed in accordance with the present invention.

[0020]FIG. 3 depicts a magnified side view of the narrow end of a bloodclot filter of the first embodiment.

[0021]FIG. 4 depicts a magnified view of a portion of the blood clotfilter showing the barbed anchor in accordance with the presentinvention.

[0022]FIG. 5 depicts a front view of the first embodiment of the bloodclot filter deployed in accordance with the present.

[0023]FIG. 6 depicts a side view of the engagement of a balloonangioplasty catheter with the first embodiment of the blood clot filter.

[0024]FIG. 7 depicts a side view of the blood clot filter after thefilter has been changed to its non-filtering state in accordance withthe present invention.

[0025]FIG. 8 depicts a front view of the blood clot filter after thefilter has been changed to its non-filtering state in accordance withthe present invention.

[0026]FIG. 9A depicts a side view of a second embodiment of a blood clotfilter using a tied suture in accordance with the present invention.

[0027]FIG. 9B depicts a front view of the second embodiment of a bloodclot filter using a tied suture in accordance with the presentinvention.

[0028]FIG. 10A depicts a side view of the second embodiment of a bloodclot filter using a unitary ring in accordance with the presentinvention.

[0029]FIG. 10B depicts a front view of the second embodiment of a bloodclot filter using a unitary ring in accordance with the presentinvention.

[0030]FIG. 11A depicts a side view an endovascular device used to changethe filter to its non-filtering state in accordance with the presentinvention.

[0031]FIG. 11B depicts a top view of an endovascular device used tochange the filter to its non-filtering state in accordance with thepresent invention.

[0032]FIG. 11C depicts a magnified side view an endovascular device usedto change the filter to its non-filtering state in accordance with thepresent invention.

[0033]FIG. 11D depicts a magnified top view of an endovascular deviceused to change the filter to its non-filtering state in accordance withthe present invention.

[0034]FIG. 12 depicts a side view of a third embodiment of a blood clotfilter deployed in accordance with the present invention.

[0035]FIG. 13 depicts the disengagement of a portion of the blood clotfilter in accordance with the present invention.

[0036]FIG. 14 depicts a side view of a fourth embodiment of a blood clotfilter deployed in accordance with the present invention.

[0037]FIG. 15 depicts the disengagement of a portion of the blood clotfilter in accordance with the present invention.

[0038]FIG. 16 depicts a side view of a fifth embodiment of a blood clotfilter in accordance with the present invention.

[0039]FIG. 17 depicts a front view of a fifth embodiment of a blood clotfilter in accordance with the present invention.

[0040]FIG. 18 depicts a side view of a sixth embodiment of a blood clotfilter in accordance with the present invention.

[0041]FIG. 19 depicts a front view of a sixth embodiment of a blood clotfilter in accordance with the present invention.

DESCRIPTION OF THE INVENTION

[0042] Referring now to the detailed drawings, wherein like numerals areused to denote like elements, a description of the embodiments will bediscussed. FIG. 1 depicts a filter delivery catheter that can be used inimplanting the blood clot filter 101 within the vena cava. The filter101 is collapsed into a small slender profile container within an outertube 103. The outer tube 103 of the delivery catheter retains the bloodclot filter 101 in this collapsed state and provides a substantialamount of the column strength of the delivery catheter.

[0043] An inner tube 105 is used to push the filter 101 out of the outertube 103. A retention hook wire 107 is attached to the filter 101 andallows the user to pull the filter back into the delivery system if theposition, while deploying the filter 101, is not satisfactory. Once thefilter 101 is completely out of the outer tube 105, the hook isadvanced, turned and retracted. A hub system (not shown) at the proximalend of the delivery catheter will allow the user to easily operate thesystem.

[0044] To implant the filter, the delivery catheter is placedpercutaneously into the jugular vein. The delivery catheter is advancedthrough the Superior Vena Cava, through the right heart, and into theInferior Vena Cava. The filter 101 can be seen by fluoroscopy. Todeploy, the filter will be held in place by maintaining position of theinner tube 103. The outer tube 103 is retracted, thus uncovering thefilter and allowing it to open. If the operator does not like theposition of the filter 101, the retention wire can be used to pull thefilter back into the sheath for repositioning.

[0045]FIG. 2 shows the blood clot filter 101 properly implanted withinthe vena cava 207. The filter 101 is an expandable structure that isnormally in the shape of a cylinder. The body of the filter 101 iscomposed of a high memory wire predisposed to the filly expandedposition. The wire of the filter 101 is formed in a zigzag pattern. FIG.2 depicts the filter 101 in its deployment phase in which it is held tothe shape of a cone.

[0046] A ring 201 holds one end of the filter together. The ring 201 canbe composed of Teflon or other suitable material that is resilientenough to withstand constant abrasion from the blood flow, but stillcapable of being broken with minimal force when desired. The ring 201restricts the end of the filter 101 to a 3 mm diameter. In thisposition, the filter will be able to capture blood clots greater than 3mm. The diameter of the ring 201 can be any diameter to adjust the sizeof the blood clots captured. The expandable nature of the filter 101will accommodate different diameters established by the ring 201.

[0047] The other end of the filter 101 is fully expanded to the diameterof the vena cava 207. Shaped as such, the wire forms a plurality of legs203 that contact the vena cava wall at the apices of the legs. Barbedanchors 205 are placed at each apex of each leg 203 to keep the filterin the intended location. The filter 101 is placed so that the conicalend of the filter 101 is just below the renal veins. The barbed anchors205 are angled so that the blood flow will impact the filter 101 andpush the barbed anchors into the caval wall.

[0048] Using a conical shape allows for the efficient filtering of theblood. The highest velocity of flow is in the center of the blood streamand most blood clots will flow through the center to be caught by thering. The legs 203 can be adjusted to vary the spacing between and legto facilitate filtering. In addition, the legs 203 of the filter in thisposition will streamline the blood clots into the center of the filter101.

[0049]FIG. 3 depicts a magnified view of the narrower end of the filter101. A tie 301 attaches the ring 201 to the filter 101. The tie 301 willhold on to the ring 201 when the ring is broken and the filter 101expands to its cylindrical form. Consequently, the tie 301 is wrappedaround the filter wire such that the tie 301 cannot be dislodged fromthe filter without breaking the tie 301. The tie 301 is also securelyconnected to the ring by creating a hole in the middle of the ring bandand looping the tie 301 through that hole. Tie 301 can be composed ofTeflon or any other material that can withstand the abrasion of theblood flow and not break from it. FIG. 4 depicts the barbed anchor thatis used to attach the filter 101 to the vena cava wall.

[0050]FIG. 5 shows the filter 101 from the front view. Ring 201 has anotch 501 that weakens the ring such that the ring 201 will break at thepoint of notch 501 when stretched beyond its limits. The location of thenotch 501 can be anywhere on the ring 201. It can be diametricallyopposed to the tie 301 to ensure that the ring 201, when broken, willhave equal portions to either side of the tie 301. The broken ring willthen be less obtrusive to the blood flow in the vena cava. The notch 501should be large enough to ensure that the break will occur at the notchand not at the point at which the tie 301 is connected to the ring 201.

[0051] When it is determined that the disadvantages of filtering bloodclots outweighs the benefits, then the ring 201 will be broken torelease the filter from its conical shape to its cylindrical shape. FIG.6 depicts one process by which the filter 101 is released from the ring201. A balloon angioplasty catheter 601 that has a large enough diameteris placed into the vena cava and inserted into the ring 201. The ballooncatheter 601 is then inflated until the ring 201 breaks at the positionof notch 501. The balloon catheter will then be extracted from thepatient's body.

[0052] Upon breaking the ring, the filter 101 expands into its normalcylindrical shape. The expanded filter is shown in FIGS. 7-8. In thisposition, the filter will hug the walls of the vena cava and not bedirectly in the blood stream to filter the blood for blood clots. Thefilter is essentially converted into a stent device. The thickenedendothelial cells around the apices of the legs of the filter willremain around the apices since the device will not be removed.

[0053] In keeping the filter within the patient and causing it to lineup against the vena cava wall, endothelial cells will also developaround the entire filter and the filter will eventually grow into thecaval wall. This will eliminate the risks that are usually present whenkeeping the filter directly in the blood stream and constantly filteringfor blood clots. Any potential risk from potential thrombus formationdue to laminar blood flow disruption and risk from device fracture orfragment embolization during the patients' life will not be present.

[0054] FIGS. 9A-9B depict a second embodiment of the present invention.Filter 101 is presented in its deployed form. Ring 201 retains thenarrow end of the filter 101 in its conical shape and is intertwinedwith the wire of the filter such that the ring will not be dislodgedfrom the filter body. Ring 201 is shown as a tied suture. Tie 301,however, is not connected to the filter 101. Not connecting the ring 201to the filter 101 via tie 301 allows the ring 201 to be completelyremoved after the ring 201 has been broken.

[0055]FIGS. 10A and 10B depict a modification of the second embodimentthat uses a unitary ring 201, rather than a tied suture, to contain theconical end of the filter 101. The unitary ring 201 is slid over thebarbed end by weaving it over and under alternating leg sets. The ringis slid fully to the opposite end where it remains in position holdingthe conical end of the filter in the constrained position. The advantageof this simple unitary ring is there is no knot that can be prone topremature failure. The ring is also the lowest profile design providingminimal turbulent formation in the blood stream. The ring in this designalso does not have a predetermined break zone that may be prone topremature failure.

[0056] The ring removal device depicted in FIGS. 11A-11D will cut thering 201 to release the filter 101 and remove it from the patient. Ringremoval device has a hook 1103 that will act to grab the ring 201. Thesize of the opening to the hook 1103 is smaller than the diameter of thewire, but is larger than the ring material. After grabbing the ring 201,hook 1103 will be retracted into the outer tube of the device. The outertube has a sharp portion 1105 that will cut the ring 201 when the hookis being retracted. Upon cutting the ring 201, ring removal device 1101will extract the ring 201 from the filter to be removed from thepatient. In removing the ring 201, it minimizes the amount of foreignmaterial present within the body to be absorbed and eliminates anypotential obstruction of the blood flow.

[0057]FIGS. 12 and 13 depict a third embodiment of the presentinvention. Filter 101 is composed of two pieces, the base section 1201and the filter section 1203. The base section 1201 is cylindrical inshape and completely lines the walls of the cava vena. Barbed anchorshold the base section in place against the caval wall.

[0058] The filter section 1203 is shaped into a cone and has a hookedportion 1205 at the end of each leg 1203. This hooked portion 1205 willengage with corresponding bends in the wire of the base section 1201.The blood flow will push the hooked portions 1205 against the bent wireto hold the filter section 1203 connected to the base section 1201. Atthe apex of the cone, a disengaging hook 1207 is placed.

[0059] To disengage the filter section 1203 from the base section 1201,a removal device 1301 is inserted. The removal device 1301 can have ahook 1303 contained within an outer tube 1305. The removal device ismaneuvered over the disengaging hook 1207 of the conical filter section1203. When inserted into the removal device, the disengaging hook 1207will engage with the hook 1303. Outer tube 1305 will contact the legs ofthe filter portion and exert an inwardly radial force on the legs 1203thereby forcing the hooked portions 1205 of the legs 1203 to disengagefrom the base section 1201. Once disengaged from the base section, thefilter section can be completely drawn into the removal device 1301 andsafely removed from the patient's body. The base section 1201 willremain within the patient's body and be incorporated into the vena cava.

[0060]FIGS. 14 and 15 depict a fourth embodiment of the presentinvention. Similar to the third embodiment, the filter 101 is composedof two pieces, the base section 1401 and the filter section 1403. Legs1405, however, contain weakened sections that are predisposed to bebroken when desired. The weakened sections can be designed to be brokenby the application of a low voltage electrical current or be aphysically weaker substance. FIG. 15 depicts the removal device to beused for the fourth embodiment in which hook 1503 engages disengaginghook 1407 and filter section 1403 breaks off at predetermined weakenedsections 1409. Once completely broken off, the filter section 1403 canbe retracted into the removal device and extracted from the patient.

[0061]FIGS. 16 and 17 depict yet another embodiment of the presentinvention. Filter 101 is composed of a single wire structure and shapedin the form of a cone to filter the blood stream. At the narrow end ofthe filter, the apex of each return bend is shaped in a loop ofapproximately 1 mm inside diameter. Stacking all of the loops on top ofeach other forms the conical end. A hitch pin 1601 is inserted throughall the loops and holds the loops and the filter legs in the filteringconical shape. The hitch pin 1601 is retains its position in the loopsby an interference fit. The hitch pin 1601 is also designed so that thepin can be grasped or hooked by a tool, pulled from its position, andremoved from the body when the physician determines that clot filteringis not needed any longer.

[0062] Once the hitch pin 1601 is pulled form the loops, the filtersprings open to its cylindrical non-filtering position. The hitch pin1601 is formed of a high memory wire in an “infinity symbol” shape withthe dimension across the shape of 1.1 mm, or greater than the 1 mminside dimension of the loops at the filter strut apexes. The hitch pin1601 also incorporates a densely radiopaque marker to aid the physicianwhile attempting to grasp the pin under fluoroscopic guidance. This“infinity” design allows the hitch pin 1601 to be pulled from eitherdirection. The physician can choose the best direction at the time ofconversion based on patient factors.

[0063] Other pin designs can be produced essentially performing the samefunction. A modification of this design is the use of biodegradablematerials to form the pin. The hitch pin 1601 can be formed from amaterial that will give a known service life and will openautomatically. The hitch pin 1601 can also be formed from abiodegradable material, which requires activation. The hitch pin 1601can be removed by infusion of an enzyme to dissolve the pin material andopen the filter.

[0064]FIGS. 18 and 19 depict another embodiment of the presentinvention. This design does not depend on a second component such as aTeflon ring or removable pin to retain it in its conical deployedposition. In this filter design, the apices at the conical end of thefilter form an integral latch. At the conical end of the filter, theapexes of five of the six return bends are shaped in loops ofapproximately 1 mm inside diameter. The sixth apex forms a pin 1801. Theconical shape is formed by stacking the five loops on top of each, withthe sixth apex inserted through the five loops. The filter is opened toits non-filtering state by grasping the legs of the sixth apex andpulling the pin back and away from the loops. The loops will slide offof the pin 1801 and the filter will open.

[0065] The sixth apex has an added densely radiopaque element that canbe easily seen by fluoroscopy and can be grasped by biopsy forceps, orother catheter based means. This design has the advantage of having nopolymer components that may weaken prematurely, and no components thatneed to be removed from the body. A latch may be formed by many otherconfigurations of the wire filter body.

[0066] The present invention is not to be considered limited in scope bythe preferred embodiments described in the specification. Additionaladvantages and modifications, which readily occur to those skilled inthe art from consideration and specification and practice of thisinvention are intended to be within the scope and spirit of thefollowing claims.

We claim:
 1. A blood filter mechanism for use in a vascular lumencomprising: an implantable filter having an active state and an inactivestate; said filter, when in said active state, being positioned to catchblood clots while said filter is implanted in the vascular lumen; andsaid filter, when in said inactive state, being positioned to pass bloodclots while said filter is implanted in the vascular lumen.
 2. The bloodfilter mechanism as claimed in claim 1 further comprising a switchingmechanism to switch said filter from said active state to said inactivestate.
 3. The blood filter mechanism as claimed in claim 2, wherein saidswitching mechanism comprises a breakable element holding said filter ina position to intercept particles in blood flowing in the vascular lumento establish said active state; and said filter switched from saidactive state to said inactive status by breaking said breakable element.4. The blood filter mechanism as claimed in claim 3, wherein said filteris biased toward said inactive state.
 5. The blood filter mechanism asclaimed in claim 3, wherein said breakable element remains attached tosaid filter after said breakable element is broken.
 6. The blood filtermechanism as claimed in claim 3, wherein said breakable element isremoved from said filter after said breakable element is broken.
 7. Theblood filter mechanism as claimed in claim 3, wherein said breakableelement is composed of Teflon.
 8. The blood filter mechanism as claimedin claim 1, wherein said filter comprises a first and second portion;said first portion being positioned to intercept particles in bloodflowing in the vascular lumen in said active state; said second portionbeing held against the walls of the vascular lumen in both of saidstates; said first portion being disengaged from said second portion insaid second state.
 9. The blood filter mechanism as claimed in claim 8,wherein said first portion is disengaged from said second portion bydetaching a hook connecting said first portion to said second portion.10. The blood filter mechanism as claimed in claim 8, wherein said firstportion is disengaged from said second portion by breaking a weakenedportion connecting said first portion with said second portion.
 11. Theblood filter mechanism as claimed in claim 1, wherein said filter isattached to the vascular lumen by a barbed anchor.
 12. The blood filtermechanism as claimed in claim 1, wherein said switching mechanismcomprises a latch mechanism capable of holding a portion of said filterin a position that interferes with blood flowing in the vascular lumento establish said active state; and wherein said filter is switched fromsaid active state to said inactive state by activating said latchmechanism.
 13. The blood filter mechanism as claimed in claim 12,wherein said filter is biased toward said inactive state.
 14. The bloodfilter mechanism as claimed in claim 1, wherein said filter comprises aplurality of filtering portions; said plurality of filtering portionscapable of being wrapped around each other to be held in a position tointercept particles in blood flowing in the vascular lumen when in saidactive state, and said filter is switched from said active state to saidinactive state by unwrapping said filtering portions from each other.15. The blood filter mechanism as claimed in claim 14, wherein saidfilter is biased towards said inactive state.
 16. The blood filtermechanism as claimed in claim 1, wherein said filter forms a conicalshape in said active state.
 17. The blood filter mechanism as claimed inclaim 1, wherein said filter forms a cylindrical shape in said inactivestate.
 18. The blood filter mechanism as claimed in claim 12, whereinsaid latch mechanism comprises a biodegradable latch pin.
 19. The bloodfilter mechanism as claimed in claim 12, wherein said latch mechanismcomprises a latch pin with a radiopaque marker.
 20. The blood filtermechanism as claimed in claim 1, wherein said filter in said activestate is sized to pass blood clots less than a predetermined size. 21.The blood filter mechanism as claimed in claim 20, wherein saidpredetermined size is three millimeters.
 22. The blood filter mechanismas claimed in claim 3 wherein said switching mechanism further comprisesa balloon angioplasty catheter.
 23. The blood filter mechanism asclaimed in claim 3 wherein said switching mechanism further comprises anendovascular device having a sharp portion capable of cutting saidbreakable element and a hook portion capable of grabbing said breakableelement.
 24. The blood filter mechanism as claimed in claim 1 whereinsaid filter in said inactive state is aligned against the walls of thevascular lumen.
 25. A blood filter mechanism for use in a vascular lumencomprising a implantable filter having a filtering portion capable ofbeing in a position of intercepting particles in blood flowing in thevascular lumen; said filtering portion having a central opening sized topass through particles less than a predetermined size.
 26. The bloodclot mechanism as claimed in claim 25, wherein said predetermined sizeis approximately three millimeters.
 27. The blood clot mechanism asclaimed in claim 25, wherein said filter is a conical shape.
 28. Theblood clot mechanism as claimed in claim 26, wherein said centralopening is at the apex of said conical shape.
 29. A method of filteringblood clots in a vascular lumen, comprising the steps of: implanting ablood clot filter in said vascular lumen; said filter having a firstshape capable of filtering said blood clots; and altering said firstshape of said filter to a second shape to pass said blood clots.
 30. Themethod as claimed in claim 29, wherein said first shape is a conicalshape.
 31. The method as claimed in claim 29, wherein said second shapeis a cylindrical shape.
 32. The method as claimed in claim 29, whereinfilter is lined up against said walls of the vascular lumen when in saidsecond shape.
 33. The method as claimed in claim 29, wherein saidaltering step is comprised of the step of: breaking an element thatretains said filter in said first shape to cause said filter to takesaid second shape.
 34. The method as claimed in claim 29, wherein saidaltering step comprises activating a latch mechanism holding said filterin said first shape.
 35. The method as claimed in claim 29, wherein saidimplanting step is performed by barbed anchors on said filter.